According to prior art, a high voltage current shunt amplifier and related process circuit may be used in application scenarios of real-time overcurrent protection (OCP), current and power protection of system optimization, current measurement for a closed loop circuit and so on. For example, in the fields of robotics, electric vehicle (EV), hybrid electric vehicle (HEV) and solar inverter, the abovementioned circuit is frequently used. In practice, information can be carried on a signal having a pulse width modulation (PWM) waveform. However, regarding circuits of the field, there are engineering problems including that input common voltages of various amplifiers vary too greatly, an amplifier is susceptible to changes of a pulse width modulation signal, and it is difficult to avoid using high voltage components. The engineering problems have caused difficulties of circuit design in the field. An appropriate solution is still required.